Most agrochemicals such as crop protection agents and many fertilizers are applied as liquid solutions, suspensions and emulsions that are sprayed onto target fields. Conventional spray technology is well known and generally understood by farmers, equipment manufacturers and extension agents. Agrochemical manufacturers and regulatory officials are becoming increasingly interested in the spray application process since it affects product efficacy and environmental contamination.
Typically, the agrochemical liquid is supplied by powered pumps to simple or complex orifice nozzles that atomize the liquid stream into spray droplets. Nozzles are often selected primarily on the desired range of flow rates needed for the job and secondarily on the range of liquid droplet size spectra and spray distribution patterns they produce. Nozzle technology has been an area of significant development work in recent years. The number of manufacturers of nozzles and the range of nozzle design, e.g., air inclusion nozzles and pre-orifice designs, have increased greatly in the past decade. The general trend has been toward larger droplet sizes as a means of drift reduction.
There are increasing concerns over inefficient agrochemical use, the cost of agrochemicals and inadvertent spray drift or pesticide run-off. Consequently, those skilled in the art have been attempting to improve the quality, precision, accuracy and reliability of application of agrochemicals. This has led to increased use of electronic control systems and GPS-guided operations. Growth in these “precision agriculture” products and strategies has lead to greater demand for “variable rate” technologies and the fluid handling means to alter spray liquid flow rates.
Simultaneously, the agriculture industry and especially the agrochemical application trade are boosting worker and capital productivity by adopting faster application speeds, wider equipment working widths and greater tank capacities. This combination results in greater efficiencies as measured in “acres per worker-day”. While precision agriculture and environmental protection often receive attention in the research and development communities and hold promise for the future, it is the productivity and efficiency aspects of application equipment that often drives immediate sales and adoption of new technology.
New sprayer models may have booms of 30 m (approximately 90 ft) widths and allow application at speeds up to 30 km/hr (20 mph) or higher. Faster ground speeds and wider spray booms can lead to application errors that are significant yet unavoidable with existing spray technology. For example, if the sprayer is traversing the edge of a field while scribing about a 100 m radius (actually, a very gentle turn), the outer nozzles are traveling 35% faster than the inner nozzles. At a 50 m radius, the difference in nozzle ground speeds is 85%. With sharp turns, such as at the end of a pass across a field, the inner nozzles will travel backwards, thereby retracing and overdosing previously sprayed areas, while the outer nozzles will significantly accelerate giving their associated land areas sparse coverage of chemical. Unless the flow rate from each nozzle is individually adjusted to compensate for these differences in travel speeds, application errors may occur. Additionally, in other agricultural spraying operations such as applying pesticide to orchard crops, the density of the foliage may vary across the tree being immediately sprayed and the operator may wish to have varying rates of spray discharged from each nozzle. Individual control of each nozzle would allow the spray intensity to be adjusted to the immediate spray target shape.
The current marketplace for application equipment includes GPS-directed rate controllers, which adjust agrochemical dose in response to field maps or prescriptions. Currently, the maximum resolution (smallest area that can get a distinct rate) for most products is limited by the width of the spray boom. Rate controllers usually control the entire boom as a unit and do not allow different boom sections, let alone individual nozzles, to discharge different rates. Increased resolution of agrochemical application and wider spray booms will require more and smaller distinct units of discrete flow rate control. Some increase in spatial resolution of variable rate application can be achieved by individual control of distinct boom sections using existing technology but the systems can involve cumbersome plumbing, wiring and operator interfaces.
A commercial system developed by Oklahoma State University and Ntech Industries (Ukiah, Calif.) applies nitrogen fertilizer using individually-controlled nozzle manifold units spaced 60 cm along a spray boom. On each nozzle manifold, three separate spray nozzles (tips) are controlled by three individual valves. When the proper range of nozzle sizes (1X, 2X,4X) are installed, the combination of open valves determines the flow rate discharged from the nozzle manifold. A 7:1 discrete turndown ratio in flow rate can be achieved with combinations of the three valves. The system requires three primary actuators for each nozzle manifold when electric valves are used or six actuators when pneumatic valves are used since each pneumatic valve requires an electric valve controlling the pilot air flow. A 30 m spray boom with nozzle manifolds at a spacing of 60 cm requires 150 individual spray nozzles and 300 actuators. Each nozzle manifold unit can be individually addressed through a CAN bus in communication with a fertility sensing system. The droplet size spectrum and droplet velocity spectrum of the emitted spray varies as the application rate is altered; however, spray droplet size is of less importance in fertilizer application than when pesticides are applied.
Many target-sensing spray control systems, such as the Patchen™ spot weed spraying system and similar commercial and research units, allow on/off—but not continuously variable rate—control of individual nozzles. Pulse width modulation, such as available in the Synchro™ and AIM Command™ systems, provide individual nozzle rate control if the electrical control systems are appropriately configured. Individual control of spray nozzles or nozzle assemblies is of growing importance in agrochemical application. As individual control increases, the need for individual flow monitoring will increase since feedback is needed for closed loop control. Even with a linear control strategy, such as the binary control of multiple nozzles or pulse width modulation, confirmation of proper flow is important.
The spray application industry is adopting larger liquid storage tanks on mobile equipment. Larger spray tank capacities result in fewer stops for refilling and greater land areas covered between stops. Assuming a 30-km/hr ground speed, a 30 m boom width and 50 l/ha (approximately 5 gal/acre) application rate, a 4000 l (approximately 1000 gal) tank will cover 200 acres in approximately 1 hour. Since the operator is unlikely to stop the vehicle and leave the cab between refillings, clogged nozzles or other problems on the boom are unlikely to be detected while significant land areas are being treated. In the previous example, a single nozzle would treat approximately 3.5 acres per tank load and a single undetected nozzle malfunction would correspond to this 3.5-acre area receiving an incorrect, or perhaps zero, dose of agrochemical. Additionally, the wider boom widths, travel speeds and vehicle sizes increasingly restrict an operator's view of the boom and the opportunities to view the boom while driving. On modern agricultural spray vehicles, 30 to 50% of the spray boom may not be visible to the operator.
On some larger sprayers such as those typically used by custom applicators in the Midwest, Central Canada and the Plains, video cameras are sometimes mounted on the rear of the sprayer so that the operator can monitor, at least in theory, the spray boom out of his or her line of sight. However, at high travel speeds, the operator's attention is fully devoted to driving instead of monitoring the spray boom in the rear, either in the line of direct sight or shown on the video monitor. Due to poor overall visibility from the operator's station and the infrequency of stops and refillings, there is a need for individual nozzle monitoring to confirm that no clogging, pinched hoses, damaged nozzles or other problems may be present or developing on the spray boom.
A similar problem exists on shielded or shrouded sprayers sometimes used in the North American Plains and in urban and landscape applications. In farming areas in extreme southern and northern latitudes and in high value specialty crops, often grown in coastal areas, the agronomic time window for pesticide applications can be critically short and often occurs during windy periods. Shielded sprayers are often used in these conditions. Similarly, sprayers used in golf course, landscape and other urban conditions commonly use shrouds, curtains or shields to deliberately obstruct the nozzles from view. This is partially to reduce spray drift but also as a concession to public relations. Some golf course and landscape sprayers are even disguised as mowers. The shields prevent the operator from visually inspecting the nozzle spray patterns to confirm proper operation. Improperly operating nozzles are not easily detected. Commercial systems for agricultural use often address this problem by routing individual liquid lines to each nozzle through a small rotameter (ball in tube) flow monitor that is mounted in the operator's line of sight. While effective, this requires cumbersome plumbing for each nozzle, and the operator must visually monitor the bank of tubes.
Relying on visual inspection (either direct line of sight or video) or simple flow measurement (ball-in-tube) does not assure proper nozzle operation. Nozzles can be partially clogged or have an obstruction in the flow path and appear to be operating correctly even if the flow rate is significantly affected. Conversely, the nozzle pattern and spray droplet size can be severely distorted by an obstruction or damage, yet the flow rate remains close to the original value. In this regard, the ball-in-tube monitors are not sensitive enough to detect clogs that could be sufficiently severe enough to require re-treatment of the spray area.
Electronic spray rate control systems and application monitors typically use a single flowmeter and/or pressure transducer for feedback of the flow conditions on the entire spray boom. In systems with many nozzles, such as a 50-60 nozzle boom, failure of 1 or 2 nozzles would be unlikely to raise an alarm since the overall effect is only 2% of the expected flow rate; the system would compensate by maintaining the correct overall flow to the entire boom. So, for example, if one nozzle in a 50-nozzle system became completely clogged, the system would simply increase the spray pressure and force an additional 2% flow through the remaining nozzles. Even with the electronic control or monitor system, the driver would likely remain unaware of the failure.
Additionally, when individual nozzle control is implemented, the need for individual nozzle monitoring increases. Pulse width modulation systems have electrical and mechanical components on each nozzle. Multiple nozzle manifolds have multiple tips and actuators at each boom location. The opportunity for failure is increased over that of a simple nozzle. These systems require not only flow monitoring but also monitoring of the control actuators used for flow or droplet size modulation. Moreover, individual nozzle control implies that individual nozzle feedback is required for closed loop operation.
Future systems may incorporate individual nozzle injection of multiple agrochemicals or adjuvants, individual control of droplet size spectra, droplet velocity or spray distribution. In each case, the need for monitoring and actuation on a single-nozzle or single manifold basis increases.
Thus, a need exists in the industry for a system and process for monitoring spray nozzle operation. In particular, a need exists for a system that is not only capable of monitoring the flow rate of a fluid through a nozzle, but is also capable of monitoring the flow pattern that is emitted from the nozzle. It should be understood, however, that similar needs also exist in other fields. For example, on irrigation systems, there may be many small nozzles, often obscured from view or in areas that are difficult to access. Failure of a nozzle might not be detected until drought damage to a plant had occurred and symptoms were visible. Likewise, in industrial spray driers, malfunction of a nozzle might not be detected until significant amounts of product have been damaged. In spray humidification or cooling systems, nozzle failures might not be detected until excessive heating or drying had occurred. Specifically, a system that monitors nozzle operation may find wide applicability in any system, whether commercial, industrial or residential, that utilizes spray nozzles.